Method of producing refractory metals



United States Patent-Q 2,822,259 METHOD OF PRODUCING REFRACTORY METALS Bertram C. Raynes, Euclid, Ohio, assignor, by mesne assignments, to Horizons Titanium Corporation, Princeton, N. J., a corporation of New Jersey No Drawing. Application August 13, 1954 a Serial No. 449,802.

' 7 Claims. (Cl. 75-841) This invention relates to the production of certain refractory transition metals and, more particularly, to the production of these metals by pyrolytic reduction of a complex fluoride of the metal with carbon or the carbide of the metal.

All attempts heretofore to produce metallic titanium by. reduction of any of its compounds with carbon appear to have met with failure because of the pronounced tendency for metallic titanium to combine with. carbon to form titanium carbide. Consequently, the recent attempts to produce metallic titanium have been directed either along the lines of electrolytic reduction or the reduction of a halide of the titanium with a metal such as magnesium, calcium, sodium, or the like. In all ofthese procedures, the metallic titanium which is produced is obtained in the form of fine particles enshrouded in a mass of various salts, and the problems associated with the recovery of this metallic titanium in a massive form have proven to be nearly as formidable as the problem of producing the metal from titanium compounds. While titanium has been mentioned herein by Way of example, it is well known that many of the other transition metals are similarly refractory.

I have now discovered that certain refractory transition metals may be obtained in themetallic state by the reduc-. tion of their alkali metal double fluorides with carbon or with the carbides of these transition metals at elevated temperatures. And contrary to expectations, I have found that the metal so produced is substantially free of carbon either in the free state or as the metal carbide. I have found that this method is applicable to the pro duction of the transition metals of the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, uranium, molybdenum, tungsten and chromium. The method of my present invention comprises effecting contact between either carbon or the carbide of one of these transition metals and a molten body consisting essentially of an alkali metal double fluoride of one of the transition metals at a temperature of about 1800 C. and higher. This contact promotes reduction of the double fluoride with the resulting formation of the transition metal in the molten body of reactant salts. However, because of the high temperature employed in the practice of my invention, which'is above the melting points of many of the aforementioned metals, it is possible by thepractice of my invention to form and collect such metals in the molten state so as to be recoverable from the reactant salt mass in a massive form.

The alkali metal double fluorides of the aforementioned transition metals may be either the sodium, potassium or lithium double fluorides. These double fluorides are stable at the elevated temperatures required in the fluorides in as pure a form as is convenient. All of these "ice double fluorides can be readily purified by conventional recrystallization techniques and even the single-recrystallized products are remarkably pure. If desired, for con trol of the fluidity or volatility of the double fluoride melt, or simply as a carrier for the double fluoride, an alkali metal halide may be admixed with the double fluoride.

The carbonaceous material which is used to reduce the aforementioned double fluorides in practicting my invention consists eitherof carbon or of the carbide of the transition metal, The carbon may be added to the double fluoride either in the form of finely divided carbon or,

' where the heat for the reaction is to be provided by an The reaction between the transition metal double fluoride and the carbonaceous reducing material can be illustrated by the following reaction which is directed specifically to the reduction of potassium titanium fluoride with carbon:

As can be seen from this equation, the products of the reaction comprise the transition metal itself, potassium fluoride and carbon tetrafluoride. Inasmuch as the metal separates from the fused salt and inasmuch as the carbon tetrafluoride is promptly evolved from the molten reaction mass, these products are formed to the extent permitted by the amount of either of the two reactants. Accordingly, it is not necessary that the reactants beintroduced 3 into the reaction zone in stoichiometric amounts provided that an excess of free carbon does not remain in the final reaction product. That ,is, it is generally advisable to use I an excess of the alkali metal double fluoride of the transi-- tion metal in order to assure complete utilization of all carbonaceous reducing material available in the reaction zone. As long as there is a significant amount ofjthe alkali metal-transition metal double fluoride available for excess of carbon 'over the amount requiredto reduce the.

alkali metal-transition metal double fluoride, the carbon or carbide present in the resulting transition metal product can be removed by using this carbon-contaminated metal either as a source of the carbonaceous material for reaction with another mass of the double fluoride or it can be used as the solid transition metal anode which is elec- 1 trolyzed pursuant to the invention described and claimed in the copending application of Merle E. Sibertet al., Serial No. 358,194, filed May 28, 1953. P The reaction between the double fluoride and the carbonaceous reducing material requires reaction temperatures of about 1800 C. and higher, and in general I have found that temperatures within the range of about 1800 to 2500 C. are effective. These relatively high reaction temperatures may be obtained by any means capable of supplying the necessary amount of heat. For example, the reaction heat may be provided by an arc struck be tween two carbon ortransition metal carbide electrodes;

Most of the transition metal carbides melt If, however, the l i n the otherhand, the heat' forreactionmay b'e'pfrovided" by externalheating' elements orby usingth'ebath itself as a resistance element by passing "currentthroughthe bath.

The reaction vessel in which the alkali metal-transition metal double-fluoride is reduced by the carbonaceous material pursuant to my 'inven'tion may be-constructetl of any'materia'l that is non-reactive with respect'toth'e' reactants at the temperature at'--which' contactis 'efiected between the'reactants and the vessel. The problem of selecting sucha material is completely eliminated, how=- vanadium, uranium and chromium (all of which have melting points not in excess of about -1900 -C.), the reaction temperature .exceeds the melting pointof 'the transition metal, the metal will be'formed in the molten state and will liquate' into a mass ofthe'm'etal and-thus-be recovered in the form of a pig. On the other handg-a less massive form of thetransition metalwillbe obtained when the metal has a melting point higher than the reaction. temperature. In either case, it may be desired to obtain the transition metal in alloyage with one or more other metals, and in this event, by incorporating such other metal or metals in the reaction .mass there will be obtained an alloy of the transition met'a'lwhich will usually have a lower melting point than that of the transition metal. Of course, the aloying metal need not be other than another transition metal, and if such an alloyage of two or more transition metals is desired it can be obtained by thepractice of this invention by using a mixture of thecorresponding'transition metal double-fluorides or by using the carbides and double'fiuorides of different transition metals as the reactants, orby a combination of these techniques.

In" addition to the production of the aforesaid transition metals, the method of my invention produces an equivalent amount of carbon tetrafluoride'. Inasmuch as the carbon tetrafiuoride does not decompose and liberate fiuorine'which might otherwise react with-the pro duced'transition metal, this tetrafiuoride'serves'a's aprotecting atmosphere for the metal as it is formed. Still further protection of the metal may be obtained by admitting to the reaction vessel a gas such as pure, dry argon or-helium-which is'-inert"with respect to the reactantsandthe reactionproducts at the prevailing reaction conditions, or a reducing atmosphere containing hydrogen may be used. Still further protection of the reaction zone maybe obtained by maintaining on the surface of the molten double'fluoride afresh charge of this double fluoride in granular form. Such a protective blanket of solid-state salt'further serves to collect and retain any volatilized salt formed in the reaction zone.

The carbon tctrafiuoride produced in practicing my,

invention can, I haVe further found, be usedto convert the transition metal componentof sucha metal carbide to the transition metal tetrafluoride (or corresponding high valence fluoride). This conversion takes place-generallyat temperatures of about 900 to l'20() 'C., particularly when l a small amount generally about by weight): of elemental: chlorine: is present. The products of such a conversion reaction-aresol-id'oarbon' and vapors of the transitionmetalfluoride, and therefore the tran'- sition metal fluoride vapors may be readily formed simply bypassing "the carbon tetrafluoride vapors through or over a body of the transition metal carbide in finely divided form under the aforementioned conditions. The transition metal tetrafluoride may also be produced by reacting the carbon tetrafiuoridewith an oxide (such as the monoxide, sesquioxide or dioxide) of the transition .meta'lkat a itempie'rature within "the range of about 1000 to 1400 C. If his desired to use the resultingtransition'metal tetrafiuoride for the "regeneration of' th'e" corresponding alkali metaLoan ition metal double 'fiuoride, the tetrafiuo'ride maybe dissolvedin dilute aqueous hydrofiuori'c acid, aand potassium fluoride is then added to the resulting mixture' to formthepotassium-transition metal double fluoride which can be recovered by crystallization or salting 'ou't' from the reaction medium.

The carbon tetrafluoride may be used in other ways to regenerate the alkli metal-transition metal double fluoride. For example, the tetr'afluoride'rna'y. bepassed into molten potassium hydroxide with evolution of carbon dioxide), and the resulting potassium "fluoride isfli'en added to a mixture or solution of the transition 'rneta'l dioxide (or other transition metal compound)v in dilute aqueous hydrofluoric acid. The hydrofluoric acid may be obtained'from an extraneous source or it may be produced by reaction between the carbon tetrafiuoride and either water *or hydrogen.

If-ithe transition metalproductobtained by the practice of myinven'tion is for 'anyreason contaminated by an excess of the transition metal carbide, the contaminated metal'ma-y be brought'in finely divided'forminto contact with a molten mass of the same transition metal-alkali metal double ifiuoride as described in the copending"ap plication of John T. Bur'well, Jr., and Quentin H. McKenna, Serial No. 398,193, filed December '14, 1953, whereupon the transition metal component of the carbide willbetransformed to one or more lower valent'transit'ion metallfiuon'des. These-fluorides are then removed from the'are'sidual carbide-free transition metal product by leaching, volatilization, or the like.

Thus, it will be appreciated that the method of my invention is particularly adapted to-produce the aforementioned transition metals in substantially pure condition-and, in the case of some of these metals such as titanium, in a massive state. It will also be appreciated that th'e transition metal carbide which is reacted With' the double .fluorideinlaccordance'with the invention may be the-carbide-which contaminates an otherwise substantially puretransition metal, and therefore the methodof' my invention can be 'used'to efiect purification of carbide-- containing-transition metals.

The following examples are'i-llustrative, but not limita tive, of the practice of my tin'v'e'nti'on':

Example I Sodium chloride was meltedby resistive heatingiin a graphitecr-ucibler When the sodium chloride was molten, potassium titanium fluoride::(:K TiF s) was added intsoliil form to this bath. The A. C. voltage on the graphite electrodes, which perfonmed the double function 0f electrode and carbon-source for the-reaction, was-"then intemperature. The-.solid-mixture was leached by simpleaqueous techniques anda finely divided, thermally produced titan um powder was recovered having a purity of about 98% .X-ray analysis of the metal powder revealed the vpresence of no titanium carbide.

Examp'leLH black was placed -iu' a gra hite crucible and a direct current arc was struck and maintained between graphite electrodes over this crucible and out of contact with the charge. Upon subsequently cooling the fused crucible charge, the mass in the crucible was removed and leached. Titanium powder of similar high purity was thus recovered.

I claim:

1. The method of producing a substantially carbonfree metal of the group consisting *of titanium, zirconium, hafnium, vanadium, niobium, tantalum, uranium, molybdenum, tungsten and chromium which comprises etfecting contact between (a) a carbonaceous material of the group consisting of carbon, carbon-contaminated transition metal and carbides of said metals and '(b) a molten body consisting essentially of an alkali metal double fluoride of said metal at a temperature of about 1800 C. and higher, and recovering the resulting metal formed in said molten body.

2. The method of producing a substantially carbonfree metal of the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, uranium, molybdenum, tungsten and chromium which comprises efrecting contact between (a) a carbonaceous material of the group consisting of carbon, carbon-contaminated transition metal and carbides of said metals and (b) a molten body consisting essentially of an alkali metal double fluoride of said metal at a temperature of about 1800" to about 2500 C., and recovering the resulting metal formed in said molten body.

3. The method of producing a substantially carbonfree metal of the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, uranium, molybdenum, tungsten and chromium which comprises effecting contact between (a) a carbonaceous material of the group consisting of carbon, carbon-contaminated transition metal and carbides of said metals and (b) a molten body consisting essentially of an alkali metal double fluoride of said metal at a temperature of about 1800 C. and higher obtained by an arcstruck between electrodes of said carbonaceous material below the surface of said molten body, and recovering the resulting metal formed in said molten body.

4. The method of producing carbon tetrafluoride which comprises effecting contact between (a) a carbonaceous material of the group consisting of carbon and carbides of a transition metal of the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, uranium, molybdenum, tungsten and chromium and (b) a molten body consisting essentially of an alkali metal double fluoride of said metal at a temperature of at least about 1800 C., and recovering the resulting vapors of carbon tetrafluoride evolved from said molten body.

5. The method of purifying a transition metal of the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, uranium, molybdenum, tungsten and chromium to effect the removal of contaminating carbon therefrom which comprises effecting contact between said carbon-contaminated transition metal in finely divided form and a molten body consisting essentially of an alkali metal double fluoride of said metal at a temperature of about 1800 C. and higher, and recovering the resulting carbon-free transition metal from the molten salt mass.

6. The method of producing an alloy of a substantially carbon-free metal of the group consisting of titanium, Zirconium, hafnium, vanadium, niobium, tantalum, uranium, molybdenum, tungsten and chromium which comprises effecting contact between (a) a carbonaceous material of the group consisting of carbon and carbides of said'metals, (b) a molten body consisting essentially of an alkali metal double fluoride of said metal, and (c) a metal with which the transition metal is to be alloyed, at a temperature of about 1800 C. and higher, and recovering the resulting alloy metal formed in said molten body.

7. The method of producing substantially carbon-free metal of the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, uranium, molybdenum, tungsten and chromium from a carbide of said metal which comprises bringing the carbide of said transition metal into contact with carbon tetrafluoride and elemental chlorine at a temperature within the range of about 800 to 1800 C., bringing the resulting transition metal fluoride into admixture with an alkali metal fluoride in the presence of aqueous dilute hydrofluoric acid with the resulting formation of the corresponding alkali metal-transition metal double fluoride, recovering the double fluoride from the resulting aqueous reaction mass, eifecting contact between the recovered double fluoride in the form of a molten body thereof and a carbonaceous material of the group consisting of carbon, carbon-contaminated transition metal and carbides of the transition metals at a temperature of about 1800 C. and higher, recovering the resulting evolved carbon tetrafluoride, and recovering the resulting transition metal formed in said molten body.

References Cited in the file of this patent UNITED STATES PATENTS 2,639,218 Anderson May 19, 1953 2,692,186 Kamlet Oct. 19, 1954 2,694,616 Wainer Nov. 16, 1954 2,694,617 Cardon et al. Nov. 16, 1954 2,703,752 Glasser et a1 Mar. 8, 1955 2,708,158 Smith May 10, 1955 

1. THE METHOD OF PRODUCING A SUBSTANTIALLY CARBONFREE METAL OF THE GROUP CONSISTING OF TITANIUM, ZIRCONIUM, HAFNIUM, VANADIUM, NIOBIUM, TANTALUM, URANIUM, MOLYBDENUM, TUNGSTEN AND CHROMIUM WHICH COMRISES EFFECTING CONTACT BETWEEN (A) A CARBONACEOUS MATERIAL OF THE GROUP CONSISTING OF CARBON, CARBON-CONTAMINATED TRANSITION METAL AND CARBIDES OF SAID METALS AND (B) A MOLTEN BODY CONSISTING ESSENTIALLY OF AN ALKALI METAL DOUBLE FLUORIDE OF SAID METAL AT A TEMPERATURE OF ABOUT 1800*C. AND HIGHER, AND RECOVERING THE RESULTING METAL FORMED IN SAID MOLTED BODY. 